A steady increase in the use of aggressive fillers and additives to enhance the properties of materials being processed in injection and extrusion molding applications has led to increased wear of conventional iron and nickel based alloy bimetallic lining materials used in injection and extrusion molding equipment.
As a result of this, a carbide bearing alloy providing better resistance to these fillers and additives was developed and because the subject of U.S. Pat. No. 3,836,341. This new alloy contained tungsten carbide particles which were differentially dispersed through the thickness of the bimetallic lining. The differential distribution of the carbides, combined with the fact the tungsten carbide particles are angular in configuration, was said to produce uneven wear rates of bimetallic lining, as well as create a "sandpaper" like effect on the outside diameter of the screw flight. Subsequently, one solution to the uneven wear problem was proposed in U.S. Pat. No. 4,089,466. The aforementioned disadvantages were overcome by the use of tantalum carbides. But shortly thereafter, an upward fluctuation in the cost of tantalum carbide made it economically impractical to manufacture such a carbide bearing alloy. These disadvantages were in turn overcome by using a mixture of vanadium carbide, tungsten carbide and tantalum carbides in the alloy as was taught by U.S. Pat. No. 4,399,198. The use of multiple carbides resulted in substantially uniform carbide concentration throughout the lining thickness. The use of multiple carbides generally solved the differential concentration problem inherent in the single tungsten carbide alloy, yet created other problems. For instance, the carbides, depending on the density, segregate into different layers, though the overall carbide concentration was uniform throughout the lining thickness (See FIG. 3 and FIG. 4). This posed machining problems, especially whenever a counterbore needed to be machined through the bimetallic cylinder. Another problems in that a significant portion of lighter carbides such as titanium carbide and vanadium carbide were dispersed in hone stock layer during the casting operation. This resulted in low volume percent (up to 20%) of carbides in the finished machine alloy. The hardness of the multiple carbide alloy is two to three Rockwell points lower than original tungsten carbide alloys.
It is therefore a primary object of the present invention to provide superior wear and corrosion resistant multiple carbide alloy.
Another object of this present invention is to provide a cylinder containing a multitude of carbides of different densities and morphologies, yet substantially evenly dispersed through each strata of lining thickness.